Makes no difference from 1-15, but when you get to 15 I'd go Fire for the mobility with Scorch. Once you hit 22 then go Frost, since you will have Shatter, Ice Lance and Finger's of Frost by this point. From about level 36 go whatever you prefer, makes no difference at this point. Personally I prefer Fire because of the Hot Streaks and mobility.

For dungeons Arcane will be best, no waiting on crits or having your damage come from Frozen targets, and you get a cleave from Arcane Barrage.

lots of misinformation here.. arcane doesnt get missiles till 22 which is painful.. also you are lacking mana regen talents which makes blast quite lol..

frost is the best lvling spec due to control and shatter..use molten armor until you get frost armor.. first glyph get glyph of icelance for cleaves.. and always use petfreeze on 2 targets or more.. spam frostbolt for the rest. frost also gets its ultimate attack at 62.. the frozen orb.. which has no limit on how many mobs it can target and has a 1 min cd.. its the best aoe in the game.

fire is the worst spec being nerfed even more.. and building an ignite while soloing or in a dungeon.. well.. lets jus say everything dies in a burst of dps.. u wont have time to do dmg as fire.

lots of misinformation here.. arcane doesnt get missiles till 22 which is painful.. also you are lacking mana regen talents which makes blast quite lol..

frost is the best lvling spec due to control and shatter..use molten armor until you get frost armor.. first glyph get glyph of icelance for cleaves.. and always use petfreeze on 2 targets or more.. spam frostbolt for the rest. frost also gets its ultimate attack at 62.. the frozen orb.. which has no limit on how many mobs it can target and has a 1 min cd.. its the best aoe in the game.

fire is the worst spec being nerfed even more.. and building an ignite while soloing or in a dungeon.. well.. lets jus say everything dies in a burst of dps.. u wont have time to do dmg as fire.

I just leveled a mage, he's sitting at 40 atm, you do not have ANY mana issues up to this point as arcane (and no evocation yet either), even if you spam AB for 2 minutes straight at 6 stacks. Arcane is OP for leveling. Frost isn't bad, fire seems kinda useless without mage bomb/combustion at low levels, but I honestly haven't even tried it yet.

For arcane, chain pull stuff with max stacks, if you get a bunch of mobs, Abarr to clear stacks and get some hefty cleave damage (nova beforehand if possible for shatter). Pulling new mobs with full stacks will allow you to 1-2 shot them. GLHF

Arcane by far. You just need to prevent your stacks dropping off and you are golden. One-shotting things all the way to higher levels.
Fire is bad for leveling atm, too much ramp up time on mobs that get one-shotted by AB6.
Frost is great but arcane is still far better.